The relationship of the structural features of the rhodopsin gene and the molecular mechanisms regulating its expression, to phototransduction and to the survival of photoreceptor cells are important neurobiological problems about which relatively little is known. The overall objective of this 5 year research plan is to characterize the molecular structure and function of the mouse rhodopsin gene. This includes studies on the regulation of its expression by genetic and environmental (light vs. dark) factors and the investigation of the mechanisms controlling its expression during development of normal mice and of mice with inherited visual defects. The amounts of mRNA for opsin and 48k (S-antigen, Arrestin) are regulated in a non-coordinate manner by light and/or the light/dark cycle to which the animal is exposed. In addition, the localization of a number of photoreceptor specific proteins in the rod inner and outer segments is transient and dependent on light. The relationship between the changes in concentration of mRNAs and photoreceptor specific proteins with respect to development, genotype, and light will be determined by Western and Northern analysis and by immunocytochemistry. The mouse opsin gene has been cloned and sequenced, and putative regulatory sequence demonstrated. Cis-acting nucleotide sequences and trans-acting factors which participate in the light mediated responses will be identified using DNA retardation assays and transfection studies. The exact chromosomal loci for the genes for mouse rhodopsin and 48k will be determined using Southern analysis of restriction digests of genomic DNA from Chinese hamster-mouse somatic cell hybrids and from recombinant inbred lines of mice. The structure and expression of these genes will be examined in mice with mutations which map at or near to their loci. The nucleotide sequences of identified allelic forms of the rhodopsin gene will be determined and the qualitative and quantitative activity of the rhodopsin gene determined for these genes alone, and in combination with mutations (rd and rds) which cause inherited retinal degeneration and transcriptional and post transcriptional effects on the expression of the opsin gene, prior to the death of the photoreceptor cells. The molecular structure and function of the five transcripts from the mouse rhodopsin gene will be determined in normal and mutant mice. The data generated by this project may increase our understanding of the normal process of phototransduction in man and/or the molecular pathology of inherited retinal degeneration.